Apparatus for suppressing interference in radio selector systems



July 25, 1933.

L. L. JONES 1,919,948

APPARATUS FOR SUPPRESSING INTERFERENCE IN RADIO SELECTOR SYSTEMS Filed March 6, 1928 I OUTPUT nv or L, 0/?

A lNPl/T iOUTPU;

T1 2. v REsoNANcE I1 llz I3 14A! 114 n LOW FREQUENCY I T INTERFERENCE 1 4A FILE]. 4- HIGH FREQUENCY I T INTERFERENCE 1 l I l 3 I4 M K! n l 5 II I lil I l I f\ v F 2: //VP(I7' Z 1 0R C1 C2 A our/ ar 7 w ur I INVENTOR Lesfer L.Jones ATTORNEYS 1 foiz r-onennLn ew VQTERSEVY i K AnrAnA'rusFon sumEssi je-mmsmsesesim name SELECTQRSYSTEMSY I 1 Application filed-'Mai'eh A i I This invention, relatesgt'o' radio q-refceiving j apparatus, 1 and I relates more particularly to a system for-selectingelectrical oscillations; c of a given frequency band fromioscillations} difiering "therefromain frequency; and has special reference to the provision of means for suppressing oscillations; differing in fre quency -frorn th'e frequenlcyO fi gdj c c c H Y Y v nore particularly described hereinafter and "band; a

is to' improve theiefliciency: of: a selector sysg c sharpenthe selectivity characteristic of such ii-0111 to timesthecircuitlresistance. It 7 is also known that asf-"the*inumber .of'cas v p 4 inductive components of 'thevarious circuits-2 alsoflin'cludingthe coupled coils forming the y I coupling transforlners M1,M2 and M3,?g11fl of; the couplings betweenadj ace'ntl' resonant v circuits being i-n the same'sense.

a decreased;

; of the invention to increase theenergy; at

'the1;desired'for selected frequency available I .pa-ratus, v v, r i Fi'gs.;2toearegraphical representations explanatory 0f:t he, operationof -thei system 0 H p diagrammatic 'vieyv- T I I showing rthe'pr'eferred 'manner of arranging V It is ,Well known jthatEshar-ply 'tuiled j i fat; the output of theselector system andto minimize the'e'nergy ofjth'e interfering or undesired frequencies;which are transmitted through the selectorfsystem[especially in i frequency bands several 5 percent} removecl from the desired irequencyband.

c cuits in cascude,.- moderately. coupled;

9 gether, will transmit a{-narr o'w,;bandi1ofire quencies :and cutoff "frequencies higher and aetance components 1 in -1 the tuned circuits ceded circuits is increase dgl the; energy avail;

' able at the outputoff the selector system. is v I 1 have found. ofithese V selector systems that an increase in the mm her oft-Lined or resonant c1rcu1ts:;beyond four r produces relativelysmall Iselectivity gains and IQlHtIVGlY-hl h energy losses. By means of the present invention, I have found that l- 7 am enabled to obtain a furthen increaefofselectivity in the system rbey ond 'thatfivhich can normally be secured vvithl four,Qtuned; circuits 'Without 1 the addition of another 1 e-prim :o j ctoft pre nt i j vent o k a systemi,-jMorespecifically, .it';is the object p p show ng the applicatlon offimyinvention to A a {selector systelnfor a radioii eceiving "apthejcircuit- "f I: Referringinowmo're in detail to the drawe ieea seriai 259,454. a.

amount I of energy available at r the output beyond that I which can be secured 'by the tuned -circuit and {with an increase in the a mentsi a'n'cljtheir relation one-to the {other as $9 ,12 11 de d n he c ai refe ne beingifhad tc] the accompanying 1 drawinghichshows the prefejrred embodiment of ,myinvention,and' inicwhich} N p r F g.1 "1 is, a, wiring-diagrammatic 'fviewor V of my" invention, and

lectorl system havinga chain of circuits such as ;1 7110 4 I inclusive ;.c', ')1'1pled together in; cas-- cade,;.theindividuall'circuits. being. adjust; Ii v ahlefsfozas to makefthe sameresonant;to the {band of'i'irequency of the oscillations desired u to: be selected-l, I; The individual cir'c'uits1 of in the form of variable condensersand the Yth hai "embady capacitive and Fi diitive I components whlch' vcom'p s the capac tive inductance. elements L1,'Li2; L3landtL 4 E; the,"

3 :I have discovered that thet'currents of ifcillations di'fi'ering from the selected hand of frequencies may be opposedor suppressed and that the currents of the resonant, os it:

lzitioigs that". is the; frequency band desired to bf select ed, maybe aidedlby theprovisiom 5 of c an auxiliary c coupling between non-adlae I cent. circuits; of the selector chain. 'Mo

ing frequencies on both sides of the desired frequency band may be substantially equal- 1y suppressed, thus increasing theselecti-v ty;

of the systeni ,;and that. thecurrents oft resonant frequencies may be augmei'iteth thus increasing the e gy a the output of the selector sy t -.The invention is especially applicable to a'chain of circuits coupled together by fixed couplings and preferablyat'optiinu nval Y ues'; Thefcou-pling' transformers M1 M2 and M3 are therefore fixed andarranged' preferably after the manner shown iingF-i g. 5- of the drawing 'as willbe explainedfurther hereinafter. To: carry out the intend-L ed object with, greatest efficacy," areal be explained further in connectionwitl i Q'and 4 'oftlie drawing, the" nuinbe of cirnarrates i:

being theone Ibelieveto' be explanatory of the results produced.

In the first CllCllll] 1 of the selector chain, fthere 1S present, besides the'currentsiof the desiredfrequencies, considerable current of the interfering or. undesired frequencies, the ratioof these currents being determined by therelative; strengths of the desired and interferingsignalsand by 'the ratio of'thc rei'sta'nce of thetuned circuitto its reactance at'thei' undesired' frequency.- .In successive tuned,v cuits'tlie interfering circuits become relativelycinuchivvealrei', and Where the LlIlClBSllGQl frequencies are diflerent from the f desiredfrequenciesby several percent, the intensity ofthe uncles red currents decreases substant ally in geometric progress on from circuit to circuit. Thepercentage difference d between desired and undesired frequencies atyvhich this phenomenontakes place is de- :termined by theifsliarpness of tuning'of the individual"circuits, assuming the circuitsto cuitsRiir-the chain "should beevenand at" be coupled @LiTOPtllTlUiIl coupling. The conleast four in number, IS Sl)O \Vi1 in ililig il' the drawing. The circuits areialso "preferably arranged so that 'there is no energy transfer between non-adjacentcircuitsex cept 1 through the couplings I tlieriebetgreen allfla's disclosed andnclaimed in my copend ing application Serxllio; 2%,790, chan e, 31, 1927', to Selector system ifor'radio" receivapparatus; The energy may be sup- '7 plied to anditalren from the circuits'in the C1 and 04-,213 shovvn inthe drawing. v

In applying my invention 'toja "fourci uit-arrangement such as shown iii-Figi'l, 'the auxiliary coupling which 'I provide is arranged between. the first and fourthncin manner disclosedin that application, Fig.1

therein corresponding; to ig i in the pres-v ent application, or simplythrough conductors connected, either side l of condensers cuits, thesaid auxiliary coupling comprising iof; the first resonant circuit the said co' beingcoupledtothe coil IA of the 'last" cii cuit of the chain, the'coupling tbetweenA and Li in a sense oppositeto the cou a coilA connected'iu series with the ele'inen ts 'pling: enistingflbetvveenj adjacent circuits,

.a The coupling between the auxiliary coils; and the inductance L4 is adjusted so as to. diminish or eliminate the residual linterfere ence bffundesired frequencies Which are 'einoyedrby several percentfrom the-desired frequenci'esi- By mean-s of this arrangeequal degrees" CO 111611 0," interference on both sides of the de sired frequency band is eliminated and'in lected frequencies are augmented.

"Tl enew results acliieved' by the circuit arrangement of my invention'may be 9X", plained" by the following 1 theory; which is nd-the currents'of the se-.

ditioii "atwv'hichfthis becomes effective appears to be that thereactance'of the tuned circuits at the undesired frequencies nust be "cascade and two ort h'reetimes the individual circuit resistance At frequencies closer to resonance than'-- these, the interfering curi'ents in the later circuits of thechain do not diminishand at frequencies very close to resonance they may .even, be greater than What might be secured with a single tuned circuit "alo11e. r I 'j fItavill be seen therefore,- that in the freyquencyrange of evvhichl am speaking there 7 exists in the lastof the chain of circuits interfering currents substantially Weaker than n'terfering currents'in the first tuned 011'- the product of the number of circuits in lOG cuiti Y couplingtlie first circuit-directly with the fourtlrI oppose-the ii'iterfering curli'eiit 'in' the fourth circuit .bysome of the fieldfgenerated by the interfering current in 1.,the first circuit. liloreover theeoupling rean aidingrelationship between the resonant or desired current in the fourth circuit and the"resonantfield of the first circuit, so that theyamplitude'of the resonance currents in i the fourth circuit is substantially increased. .igThis: cifect'gcanbe secured. with a chain 'of' three or five circi its coupling the first to the last, but only with a diminution of interference on one side ofresonance and an increase of interference on the other side of resonance; A'deeper insight'into the underlying Telationships explaining the diiference in results-obtained with evenand odd numbersof cascadedcircuits can be had by consideration of the vector showingsin Figlures 2, 3,'and 4.

. In'Fig. 2 of;thekli'awving, U; indicates the resonance current in circuit 1. Assuming 'thati'crcuits l and 2 are coupled (in a given iio quired toproduce this opposition produces law a of the resonance] current in circuit '2 :{w'ith 5' respect to '11. Circuit 3 being similarly oot-- pled "to: c-ircuitE Q; that is stirthatthe-voltage; 7 induced in 3. also]. lags; 13 represents; the

i phaseof the iesonence currents in circuits Similarly I l represent-stile phase of th'e lresone-lice current in circuit *4. "NQOW, ifacOu-Q x pling be,pi-ovided "between circuitsv I andil, in the sense oppositeor'revers'ed toqthe-couplings betweeniadjacent circuits that is" the coupling b'eing 'such that the vcltageinduced current induced in circuit 4' directly from circuit 1 will be phased aSgshownfiby the vector 14A 7 Thisbeing'in the same'clirection-r i V asl4 is additive therewitlnand explains the .pling of this inventien.)

corresponding set 01? i ecters'shbwingthere Q lationshlpsflexistiug betweeng-thef interfering,

'i currents of frequencieshigher-tha'i'theres onantv trequencypl Assuming ithewph asefof' the interferingcurrent"1n circuit 1 to ,be, as

shown in II, the interfering current in cirf cuit Quill be as, shewnhyll; Thi because thegvoltage in 90 behind the current inlcir' cause circuit 2 pi'esentsvaninductive jreat .-a1.1ce;.to the -higheri,.:irequencya interfer currents. {This phase: an'gleeis sulist'antizj iy 90 because we have postulated-[that the' reactance of the circuit to hese; interfering frequencies is Scrxinoj in es the "cir cuit resistance. Similarly ,th rents, in circuits; '3 and n 4 are asshow'n by; 182

I and PL Now the yoltage induced nteci cuit jby the direct{coupling Withmircuit;11

{leading thecurrents incircuit- 1:1 Since the intcrferin l current 1n circuit 4 lags behind the f i ndu'ced Voltage the interfering current n Will be phased'asishown by letA, or oppcff sitely to theinterferiiigcurrent due t'o 'the *thi ci'igh the 1 intermediate 'tu'neda adjusting the direct coupling between circuits '1 and 4..c ur-.f j x rents I4 and Il-A' mayfbe igmade to substancoupling g A circuits. i Then by suitably tially oppose each cumandfso' reduce the interferingenergyto avnnnimum.

duet thefcon'pling between the adjacent Aci r- 1 c :cuit; teadsnan by 'substantiall-y 90 givi-v leads the, current {115 thenthe vclt ge;

increase in resonance current: duetojthe con quencj i. 1

11 ed into circuit. 2 i uit 'lt a nd the i interfering ;current in circuit 2 j=1ags sub-- stantially ==90 behind the, induced Voltagebe-h ivillbe phased as shown 134A, since this j coupl ng arrangedt0 produce voltages terfering"frequencies and therefore; the ins "te'rfefring currents in themlead 'theinduced voltages by substantiallyf909, thereby compensating for the lagging induced voltage -cui,ts.- Similarly JEAA" represents; the lead-- in TphaSe oi' thevoltage induced directly into c rcuit {lrfromthe interfering current in circuit: '1; 1Tl'ie..eurrentinduced-thereby in 7 woluld give rise to oppositely phased 'inter'. 'lerence components, which Would assist the low: frequency interference and diminish the high .jfrcquencyinterference ithflthecou i pl ngs arranged as desc'ribed flabove. Rel Yver'sin'g' any "one" of the lceupli'ngs .would niei relylseri 'e t9 change the; assisting-inter V omponent jfroin'lou ito high :fre-

The edditlonal or auxiliary 'coupling be-: tween the firsta'nd fourth circuits maybe made; ed at a:valueindicat'edibya majority -of jez iperience case's found? to be *de-'' s'irabler or it "may beinade; variable; over a mo'derate range'under the control OffthetI-Vi-t Ire'c'eiving :-set operator so as to beexactlyj -adjustable. to meet "anyspecial: case ofirew 7 sidual interference. V In Fig.5 of thedrawing, Iishowa pre-f r-ei-redwt cf: fixedly-adjusting the cou c pl-ings between 7 adj acen-t circuits witha maxi:

Y mum or eptimuni degree ofcoupling; Y i jzmeanspf themethod shown in Fig. 5.;of thedra Wing, I am enabledt0 construct a Simple and'inexpensive Wayaselectorsystem in which substantial optimum coupling. may be t lnaintainedover a wide frequencybandwith out "the necessity of making any manual adjustine'n tsv between the circuitsm "The indie: vidual'i-cii'cuits of the selectorgchain 'designated by re'fierence characters similar to that used fcr F g'." l of the. drawing are first couple together and. the degreeofnductive coupling adjusted so that atthelowest fre-. quencyjof the bandthe couplingsare slightly less than e optimum ,value. 'I'then' tune to the hinest frequency of theQba'nd for which a l; selector is designed and sup le: n ent'the inductive coupling of each circuit with 3a capacity coupling designated by the condensers K1, K2 and K3, the supplemental:

icbupling functioning to increase the coupling between adj acent: cireuitsto the higher degiiee 1 necessary "for the optimum coupling. atthe highenfrequencies:"Now returning to; the lower. frequencies, it Will be found that thisjkadditional capacity ,c'oupling fpifoduces. little change inthegdegree of c'oupli'ng and sufiicientf only: to bring; the total Q' coupling,

to 1 e6 "cuits suchas, for'example, between I and '3,.'

7 to the mean frequenoy oflthe oscillations to p be selected, and; means for suppressing the oscillations; of frequencies 3 outside "the seilectd hand, saidmeans comprising an 'auX- v iliary coupling between 'nonadjacent ,-oir-. cuits of the chain coupled in asenseo'ppo site to the couplingbetween adj ace'nt circuits of the chain:

Y 3. A system- ;-ior.,selecting electrical oscil-. lati'ons of a given frequency band fromros-f cillations differing tl.1ere'roin in frequency comprising ;a chain iotc rcuits' coupledj n I cillations of 'frequenciesoutside, he selected band, said means. compris ngQangauxihary coupling between non-adj acent; circuits of 4. A t -syste'm for selectingelectrical oscil-i lations of a given frequency vbandf from 'osil cillations differing lthereirom in frequency comprising a chain of *at least four circuitsj resonantv to the "frequency-of the oscillations t "to be selected and coupledfin'one sense 1 cascade, and means for su pr ssingthemeicillations "difiering in frequency from theselected 'band, said fmeans {comprising an: auxiliarycoupling between the. first andlthe last circuitsof tlie cl1ain coupled a se'nsei opposite-to the 'coup'lin.g-between adjacent 7 circuits of thechain. v V l 1 5. A systeln for selecting l electrical oscil jlationsof, agiven frequencyband from oscillations "differing" therefrom; frequency. f comprising a chain-of circuits coupled; in. cascade and: all tuned alike and resonant to the mean fr equencyrgoi the oscillations. to rbes'elected', and ailcoupling]. between non-afd j jac'ent, circuits of the chain so re1ated to r f'theeoupled circuitsofthej chain as to sup- {press the interfering oscillationsi' of-Lfre of the oscillations to Eta-selected, the react-p ance of the!resonantdiicuitsto undesired" frequencies beingjtheiproduct of the number 7 of circuits and V jail least twice the resistance of an individual icirouit, image; coupling. between non-adj acentilcircuits 10f thelchainj: related to the 'coupledreircfuits, ofithefchain .to asubstantiallyequally suppres'srthe inter- I fering osci1'1ations onboth sides-of the ire-j 'quencyband selectedgn p 7 '73 'A s'ystem for;selectinginv geometricali "6. system progression electrical oscillations of i a given frequency band from oscillations -differingi therefrom. in frequency comprisingljrafchain z of circuits coupled 1 in cascade, .anClQ all tune quencies ,outside the 'sele'ctedband onboth aside'sof the selected. band'ifsubstantially q al y-' for selecting; njlg'eometrical alike and resonant, :t Jthe mean frequency :1 A; system for selecting in; geometrical progression,electrical oscillations-eta given v a frequency l handj'from oscillations.differing- Li. ctherefronifin" ifrequency' comprising a chain of-an; even number andat least four circuits toebelyselected {and 'coupledincascade, the saidcircuitsfheing fixedlygcoupled with sa 9 maximum (coupling, and'means for opposing frequency band from oscillations.differing,

therefrom frequency comprising a chain 10f fourxor greatereven' number of -circuits. 7 t to be selected and'coupled in cascade, the reactance offthe resonant-"circuitsto'undew V sired; frequencies being theproductfxof the; 4 number of circuits and; at least "twice; the

resistance of an individualcircuityand an;v auxiliary coupling between the first and last '7 v circuits of. the chain-irelatedto the coupled resonant to the frequencyof the oscillations circuit-s of the chain and adjusted to sub;

.sti'antiallyj equally suppress 1 the interfering oscillations onjboth sides'ofthe frequencyv band selected. r

progressionelectrical oscillations ofa given; iv

8.1L systenifor' selecting in geometrical progression electricalv oscillations 'iof .a given i frequencyhand from oscillationsdifi eringgj tlie refrom in frequencycomprising ra chain I of circuitsi coupled in cascade and all-tuned" alike andw resonant to the mean, frequency .ofthe oscillations to be selected-,and means '1 for opposing the currents of oscillations 30f frequencies -outside 'the 'selecte'd band Tandy for aiding the currents of tl1e.res0na1'1t;os}f

cillation'sf, said means} comprisingi an au'xiliary coup'ling betweeii selected non-adjacent i I a I rGllCLlltStofltllepllalll. 5

resonant to the! frequency; of the oscillations the currents i-ofoscillations .z difier'ing from 'the selected; bandfandforaiding the; currents of the resonant oscillations; said; means ooin prising" an auxiliary coupling between the first and the last circuits} of the, Ichai n'coupled' in; a fsense oppoisiteito thefcouplings= between adj acent circuits v (if the chain, the: I

reactance of, the-resonant circuits "to undel resistance. of an; individual circuit i lnicomhinatloln agpair. of resonant cirsired .frequencies heingxtheproduct of the number ofc ircuit's and atileastgtwi'ce the q cuits'l each comprising a fixed; inductance and; v

a. Variabletuning condenser. arranged in series therewithfifor tuning said circuits over} a predetermined;frequency band, said cireuitsl'being;tuned"alikeand inductively-cons. j I ple d together and a relatively smalleapacity I f i'coupling insuificientito substantiallyaifect: I

tlietuning of the circuits and supplementing the inductive coupling j between the circuits,

the capacitive andjin'ducti-ve couplings be-:

f 'ing 'related to" produce optimum coupling over thesaid predetermined frequency band; j

' ,tnsrnnnJonns -x my v 

